History: While it may seem a bit odd to consider a spiral of pure energy that radiates outwards in ways that nobody really understands as an adversary of The Doctor, the Mandragora Helix is sentient, although in what way and what kind of life form dwells in the centre is something that nobody is entirely clear on. It was recently revealed that there are other such intelligences in existence - a scientific theory speculates that a powerful sentient force was caught in the Big Bang and dispersed across the universe -, but some of these dwell within planets to serve as a ‘timer’ measuring how long these planets will exist depending on various environmental factors rather than existing on their own.

Regardless of its origin, the Mandragora Helix first encountered the Fourth
Doctor as he was travelling
with Sarah
Jane Smith, pulling the TARDIS towards it and then sending it down to Earth in the fifteenth century - apparently contemporary with the Helix at the moment when The Doctor fell in to it - containing a sample of Helix Energy in the form of a ball of fire that burned whatever it touched.

Seeing
Man as a potential threat to its control over its domain in the future,
the Helix possessed the body of Hieronymous, a self-proclaimed seer
who was also the leader of the forbidden cult of Demnos, intending
to organise the cult into an attack on a masque organised by the
young Duke Giuliano, whose interest in the sciences had led to him
holding a masque at which were some of the great thinkers of the
age, including Leonardo Da Vinci. The Helix energy tried to eliminate
The Doctor before striking at the masque, but The Doctor was able
to see through its attempts to hypnotise Sarah and break her free
of the control. Using a breastplate connected to magnetically charged
lines of energy, hidden under his normal clothes, The Doctor was
able to drain off Hieronymous's life energy - the Helix' control
over him having progressed to such a point that he was composed of
pure energy - and then, posing as Hieronymous, destroyed the cult
by releasing the last of the Helix energy into the Earth, taking
advantage of the fact that it was currently weakened due to being
divided amongst the various members of the cult. However, he knew
that, in its current orbit, the Helix would eventually be in a position
to attack Earth at the end of the twentieth century....

The Eleventh Tiger
(David A. McIntee)

Over four hundred years after this confrontation,
it is implied that the Helix had another encounter with The Doctor; specifically,
the First
Doctor, currently travelling with Ian
Chesterton, Barbara
Wright and Vicki.
This encounter occurred in China in 1865, when The Doctor and his companions
found themselves dealing with a sentient, helix-like
energy source that was arriving on Earth by exploiting a
stellar conjunction occurring every two thousand years to come to Earth.
The last time this
conjunction had occurred, it had convinced Qin Shi Huang,
the First Emperor of China, to imprint his mind into an executable application
engram recorded
as a stone tape recording, along with his two generals, which
were then imprinted on the minds of warrior monks during a lunar eclipse.
Although
Qin believed himself to be the original Qin, re-establishing
his old army and seeking to regain his old power over China by conquering
various
territories and capturing and executing the alchemists, astrologers
and teachers who would support the English forces present, there were
suspicious
gaps in his memory which were noticed by Barbara, demonstrating
that the intelligence responsible for his revival had erased parts of
his
memory to make him easier to control.

Realising
where the Helix intended to transmit its energy to launch its assault
on humanity based on Qin’s recent conquests - the territories
he had taken were seemingly randomly selected from a military standpoint
but instead served as sacred sites that could channel the Helix’s
energy - The Doctor and his companions (Aided by Ian's great-grandfather,
who had briefly been mistaken for Ian's future self due to the family
resemblance) tracked down the location. While Major Chesterton's
forces destroyed the Helix's stone henchmen with hammers and other
blunt instruments, The Doctor was able to short-circuit the Helix
by breaking its control over Qin long enough for him to step into
a pool of water; since the Helix's powers were based on electricity,
this threw off the Helix’s influence on its agents, preventing
its energy being transferred and ending its second attempt at conquest.

(Notes: The Helix is never referred to by name in "The
Eleventh Tiger", but the
odds of there being anything else in the universe that is so identical
to the Helix are too great to be a coincidence; the energy force
here knows The Doctor, can possess humans and revert them to glowing
yellow energy, it wants mankind's teachers and great minds killed,
and was defeated around four hundred years before the First
Doctor's
encounter with it here, the Tenth
Doctor later positively confirming
the Helix’s presence in this time during his confrontation
with it in "Beautiful
Chaos").

The Helix’s first attack on the twentieth century eventually
occurred, in a rather different fashion from the Helix's original
attempt, in The Doctor's Seventh incarnation. At this point, The
Doctor, puzzled over the statistically significant number of recent
alien visitations to Earth, realised that the Helix still maintained
a degree of control over the TARDIS, and had been steadily growing
in power over the years until it possessed the strength to not only
draw The Doctor to Earth, but also a wide variety of other alien
species that would normally have never even come near the planet.
While exploring the TARDIS's warped corridors, The Doctor and Ace discovered a door to the Falling Star nightclub on Earth, there running
into two UNIT soldiers investigating a case of drug dealing of a
new drug called Mandrake.

Investigating further, The Doctor realised that the Helix was using
the TARDIS as a link between Earth and the Vortex, and that the Helix's
'agent' on Earth - Stranks, the owner of the club - had been selling
Mandrake as it sapped the willpower and made people willing slaves
to the Helix. The alien encounters had all occurred because the Helix
wished to observe The Doctor in action, and thus gain an idea of
how he would react in any given situation; it was now confident that
it could out-think any plan he came up with. Summoning the Helix
to Earth, Stranks explained that, as the Helix's power grew, it would
consume the Earth and transform it into another energy helix - and
the two combined would form a double helix of pure energy capable
of reproducing itself and consuming the Universe. At the final moment,
The Doctor was powerless to help, but, fortunately, the TARDIS was
able to throw off the Helix's control and dematerialise, breaking
the link with Mandragora and saving the world (Although there was
a brief period where the TARDIS seemed to have saved the Universe
by disintegrating).

Beautiful Chaos
(Gary Russell)

The Doctor faced the Helix for a final time in his Tenth incarnation
when he took current companion Donna Noble back to Earth on 15th
May 2009 for the first anniversary of her father’s death. Taking
a casual wander around the streets, The Doctor noticed a new computer
sytem called M-TEK that had been recently launched by the company
MorganTech, followed closely by a group of people gathering at observatories
that had been monitoring the newly-appeared ‘Chaos Bodies’-
new stars that had seemingly appeared out of nowhere - in various
constellations. Quickly identifying the Helix as the source of this
latest attack - the true Helix on this occasion, rather than the
fragments that he had encountered in the past - The Doctor determined
that his attempt to earth it had actually trapped it in the ground,
forcing it to spread out trying to repair itself until it managed
to make contact with the DNA of some people in the immediate vicinity.

Waiting patiently in the DNA of its host families as
they spread out across the world, the Helix finally struck in 2009,
intending to lure The Doctor to its ‘base’ in MorganTech
- it having helped Dara Morgan establish his business so that it
could expand outwards - so that it could use his body as a host,
allowing it to lead humanity in expansion across the universe; having
realised that it couldn’t destroy mankind, it would now become
part of it. However, using a reprogrammed M-TEK computer, The Doctor
was able to broadcast a signal that disrupted Mandragora’s
control over its agents before destroying the computer terminal it
used to appear on Earth, weakening the main source of the Mandragora
energy and forcing it to use the body of Netty Goodheart, a friend
of Donna’s grandfather Wilf, as a host (The Doctor was too
strong and it believed that Wilf had a heart condition). Taking advantage
of Netty’s Alzheimer’s, The Doctor was able to weaken
the Helix by forcing it to expend so much of its energy repairing
Hetty’s damaged synapses to allow it to think that it soon
lost the ability to control her. Forced to depart her body, the Helix
retreated back into space, its mental energy already collapsing due
to exposure to Netty’s damaged mind, leaving it no further
danger to humanity.

A few years later, The Doctor’s former companion, Captain Jack Harkness, learned that Earth was actually the ‘host’ for another Helix Intelligence, this one dwelling within Earth - apparently trapped at the core when the planet was created -, ‘monitoring’ Earth’s environment, along with factors such as global warming, species extinction, and others ("Exodus Code"). Typically this intelligence should have been content to lie dormant and leave Earth to continue for at least a few more centuries despite the environmental damage humans had caused in recent decades, but this system was apparently disrupted when a lost Incan tribe attempted to sacrifice Jack in an old chamber as part of an ancient prophecy, Jack’s fifty-first century physiology confusing the Intelligence. When Jack’s blood was re-introduced to Earth to end the Miracle ("Torchwood: Miracle Day"), it apparently gave the Helix Intelligence new strength while ‘convincing’ it to accelerate mankind’s ‘expiration date’, causing various geological eruptions and seismic upheavals across the globe, as well as releasing a mysterious pheromone into Earth’s atmosphere that caused various women to act in a deranged manner if they possessed the right gene sequence and hormone imbalance, apparently trying to use the chemicals to attract Jack’s attention and draw him back so that it could gain the strength to escape (Jack speculated that this Intelligence had been on Earth so long that it had absorbed mankind’s anger and hatred and was now so angry that it wanted to escape regardless of the cost). Returning to Peru, Jack attempted to return to the centre of the Earth and convince the Helix Intelligence that it had made a mistake, only to learn that he had made a mistake; the Helix Intelligence actually needed his blood, along with the blood of two other sacrifices, in order to heal itself from the damage caused by recent events. With the woman who had attempted to sacrifice him and a holographic A.I. duplicating Gwen’s physiology down to the cellular level - Jack refusing to sacrifice the real Gwen or a child who were the only other ‘candidates’ -, Jack entered the pit and healed the Helix Intelligence, although it subsequently took days for him to dig his way out.

Parts of this article were compiled with the assistance of David Spence who can
be contacted by e-mail at djfs@blueyonder.co.uk